(a similar thread has already been posted on another forum, but I believe that this tool is so great that it's worth publishing here as well, however in a shorter form to avoid duplicates) TinEye This looks like a great tool for designers, developers, website owners, etc. - you can search the web for copies of your artwork to ensure your hard work is not being copied/stolen. Note: TinEye is still in beta and using it requires sign-up.
I signed up, installed the firefox add-on & tested it out. Very Nice engine. I'll be using it along with my monthly copyscape checks